Absolutely. TV is so different now it's hard to remember back to what it was like before Letterman, and to recall that Letterman the old curmudgeon was once the edgiest, most innovative and closest to "underground" thing on network TV.
SNL had opened the door to a new sensibility of TV comedy, but Letterman burst through the door and ran. On Johnny Carson's show (and how I loved that show), he would kid around with movie stars and comedians, but there was always a veneer of respect for the institution of show-biz. Letterman's attitude was: That's all phony bullshit, and we all know it. Can stagehands and NYC weirdos be as entertaining as movie actors? Letterman's answer was, of course they can. Should a host fawn over guests and praise network bosses? Not on Dave's show, because the audience recognizes when something's real and they'll take real over fake any day.
Tom Snyder had done OK with Tomorrow, but it was a niche thing. Late Night made the 12:30 slot not only relevant, but hugely profitable. Letterman was the only name that could break NBC's Tonight Show dominance, and because of NBC's blunders he did just that. Leno and Conan inherited shows, but Letterman made a new show, and a new kind of show, from nothing. He will be remembered as a pioneer of TV. It will be interesting to see what he does in retirement.
As if that had any real life implications.